As is known, electric motors include a stator and an armature (or rotor) with windings thereon. The motor is designed so that electrical current through the stator and armature windings will generate opposed magnetic fields. Rotation of the motor shaft occurs as these magnetic fields attempt to align.
In a DC motor, it is important that the input provided to the motor windings be a stable DC input having no AC component. Accordingly, it has been common practice in the industry to use a capacitor in the motor input circuit for suppression of radio frequency interference (RFI) and conducted voltage transients. Typical capacitor assemblies currently used in electric motors for reduction of RFI and conducted voltage transients have solid lead wires attached to the capacitor terminal plates and are epoxy dipped to provide insulation and strain relief for the lead wires. The capacitor is attached in parallel with the motor input terminals through the lead wires, the lengths of which are often dictated by the motor circuitry packaging. Generally, the capacitor lead wires are assembled to the motor circuit by welding, soldering, or through a splice connector.
It has been found, however, that the effectiveness of the capacitor to suppress RFI and reduce conducted transients depends directly on the length of the lead wires. A shorter capacitor lead wire provides greater RFI suppression and lower conducted voltage transients. Nonetheless, due to the physical constraints of the motor circuitry packaging, the prior art has failed to effectively minimize the length of capacitor lead wires to achieve the maximum possible suppression of RFI and conducted voltage transients.
Accordingly, there is a need in the art for an electric motor input circuit which eliminates the effect of capacitor lead wires on the suppression of RFI and conducted voltage transients.